The latest Forgeworld newsletter brings more Mechanicus goodies n the form of Battle-automata! Take a look at the pic and description from Forgeworld below:
The powerful Castellax pattern is the most common of the widespread Castellan-type Battle-automata in service at the outbreak of the Horus Heresy. A general battle unit developed by the Legio Cybernetica during the Great Crusade from its ancient forebear, it is primarily intended for siege work and shock assaults, and is heavily armed and armoured, with a notoriously aggressive and responsive machine spirit, which has fashioned for it an enviable reputation on the battlefield.
The Castellax, deployed in units of one to five by the Legio Cybernetica, has a standard configuration of bolter and bolt cannon armament, and is able to maintain a punishing barrage of firepower as it advances.
There is also the Magos Dominus with a Rad-Clenser to add to your Horus Heresy army: